1. Field of the Invention
The present invention relates to multi-line wireless telephone systems and, in particular, to techniques for ensuring communications despite power losses and irregularities.
2. Description of the Related Art
The use of telephones and telephone systems, including wireless telephone systems, is widespread. In wireless telephone systems, one or more cordless or wireless telephone handset units communicate via either analog or digital radio signals with a base unit, which is typically connected via a standard telephone line to an external telephone network. In this manner, a user may employ the wireless handset to engage in a telephone call with another user through the base unit and the telephone network.
Multi-line wireless telephone systems are also in use in various situations, such as businesses with many telephone users. Such systems employ a handset that communicates with up to N handsets simultaneously, typically with digital communications schemes, such as a spread-spectrum, time division multiple access (TDMA). In a TDMA system, a single RF channel is used, and each handset transmits and receives data during a dedicated time slice or slot within an overall cycle or epoch. Efficient power use is important for a wireless system since the handsets are typically battery-powered. The base unit typically requires more power to operate than the handsets, and is thus usually powered by an external AC power supply. Irregularities may occur in the AC power, such as a loss of power or momentary power spikes or glitches, which can cause communications to be disrupted. For example a power glitch may cause a loss of TDMA synchronization.
UK Patent App. No. GB 2 279 827, published Nov. 1, 1995, discloses a base unit which recharges a batter on a battery-powered portable unit (such as a cordless telephone handset) via a first current source and a first port, can simultaneously recharge a spare batter pack for the portable unit via a second current source and second port, and a back power supply switch can connect the spare battery to provide power to the base unit on failure of an external power source which normally provides the power to the base unit and for charging the batteries.
A wireless telephone system comprising one or more wireless handsets and a base unit. Each handset has a handset transceiver and a rechargeable handset battery for powering the handset. The base unit has a base transceiver for communicating over an RF channel with each handset via its handset transceiver; a recharge cradle for physically docking a docked handset battery comprising one of a detached handset battery and a handset; and a recharge unit for recharging the docked handset battery. The base unit is coupled to an AC power supply and utilizes the docked handset battery as a backup power supply if AC power from the AC power supply is lost or irregular to prevent communication between the base unit and the handsets from being disrupted.